Cryptococcus neoformans is a pathogenic yeast belonging to Basidiomycetes, a taxonomic Class phylogenetically remote from the rest of pathogenic yeasts (Ascomycetes). C. neoformans causes fatal meningoencephalitis primarily in patients with T lymphocytes dysfunction and it is the only species in the genus Cryptococcus that has optimum growth temperature higher than 300C. Although extensive studies on the molecular bases of cell cycle and morphogenesis have been carried out in ascomycetous yeasts, no such studies have been conducted in C. neoformans. This project was initiated to study molecular genetic regulation of cell cycle in C. neoformans. We have cloned a homolog of Drosophila CRN gene by complementing a C. neoformans strain of serotype A which was isolated from a localized granulomatous lesion produced in the nasal cavity of a cat. The isolate failed to grow at temperature beyond 350 in vitro and produced hyphal elements in addition to yeast cells in the feline nasal tissue. When the isolate was transformed with the C. neoformans serotype A genomic library, a clone containing transforming plasmid with an insert homologous to the Drosophila CRN gene regained the phenotype of a wild type C. neoformans grew at 370C in yeast form with no hyphal element. A homolog of cyclin-dependent kinase family member(PHOA) required for developmen of sexual reproduction in Aspergillus nidulans was cloned from a C. neoformans serotype D isolate